One of the major challenges associated with the use of brackets for orthodontic treatment is the removal of the brackets from the teeth of the patient. Metal brackets are generally removed by pinching the bracket in a generally mesio-distal or diagonal direction using a pair of pliers, such as so-called Weingart pliers. The pliers apply compressive forces and pinch the brackets generally in a mesio-distal direction, typically by placing the jaws of the pliers diagonally across the bracket and engaging the tie-wings at opposite corners of the bracket, for example, at the gingival/mesio and occlusal/distal corners of the bracket. Pinching the bracket in this manner results in deformation of the ductile bracket body as well as the debonding pad used to attach the body of the bracket to the tooth surface. This deformation causes the interface between the adhesive and the bonding pad or bracket base to separate or fracture, thereby essentially peeling the bracket away from the tooth surface as the adhesive material debonds.
Brittle orthodontic bracket materials, such as ceramic materials, are much more problematic during the bracket debonding process. These bracket materials are extremely hard and non-ductile relative to materials, such as stainless steel, typically used for metal brackets. Ceramic materials also have a low fracture toughness relative to steel and other metals, meaning that ceramic material is much more prone to fracture, rather than deformation, under an applied force. An attempt to pinch the tie wings of a ceramic bracket in the manner described above for metal brackets generally results in fracture of the tie wings or other portions of the bracket due to point loading of the bracket material by the pliers at the contact points.
For these and other reasons, such as heightened sensitivity to surface imperfections, various tools and methods have been proposed and used for debonding a bracket from a tooth. However, many tools and/or methods have not been fully satisfactory. For example, plier-type tools having metal jaws with sharp, opposed edges have been directed into the adhesive interface between the bracket base and the tooth. These tools separate the bracket base from the tooth surface by applying force directly to the adhesive interface.
U.S. Pat. No. 4,904,183, issued to Hannan, discloses a torquing tool having slotted ends which closely fit over the mesial and distal bracket surfaces. The user applies a twisting force about an axis generally normal to the bracket base and tooth surface to fracture the adhesive bond therebetween. This reference discloses that the tool is especially useful with brackets made of brittle, ceramic material.
U.S. Pat. No. 5,062,793, issued to Cleary, discloses a debonding instrument having a pair of arms with pulling sections adapted to engage a bracket behind its occlusal and gingival tie wings. The arms are connected to a lever, and movement of the lever enables the arms to simultaneously exert a pulling force on both of the wings along substantially their entire mesial-distal width in order to lift the bracket from the tooth in a straight-line fashion.
However, a torsional force, such as the quick twisting force or motion disclosed by Hannan, to be applied to the patient's tooth can be very uncomfortable for the patient. Further, depending on the bracket material and bond strength, these methods often require an excessive amount of force making it difficult to separate the bracket from the tooth. Such excessive force or methods may result in damage to the tooth surface or increased discomfort. Accordingly, dentists are hesitant to use such force, particularly in a torsional or pivoting action, to debond brackets.
U.S. Pat. Nos. 5,366,372 and 5,439,379, both issued to Hansen, disclose an orthodontic bracket having mesial and distal sections debonded from the tooth by pivoting the sections toward each other in respective arcs about a central reference axis extending in an occlusal-gingival direction. The mesial and distal sections are discrete and spaced apart from each other, or alternatively, integrally joined by a relatively thin web that bends and optionally fractures upon debonding. However, such design, when debonded by dentists may result in breakage or fracture of the bracket, even with less force than traditionally required, resulting in discomfort, and presenting potential harm from the pieces of the broken bracket in the patient's mouth.
An improved debonding technique has been described in U.S. Pat. No. 6,382,965 and discusses the use of a pivoting or rocking motion to break the bond between the adhesive and the bracket base. While this method has been quite successful, it would still be desirable to further decrease discomfort to the patient during debonding. In particular, it would be desirable to further reduce the amount of force needed to remove the bracket from the patient's tooth while retaining the necessary bonding forces during the orthodontic treatment. Another goal is to decrease the chances of having a nonmetal bracket break during debonding.